Investigation of transformations of low-grade manganese ore during the roasting process

Abstract

The transformations of low-grade manganese ore were investigated during roasting in the air at different temperatures up to 1200°C. The transformations were followed up by XRD and TGA-DTA. Moreover, the morphology and magnetic properties were determined by SEM and VSM. It was observed that MnO₂ transformed to the lower oxide Mn₅O₈ at 500°C and then to bixbyite (Mn₂O₃) at 600°C. Finally, the bixbyite decomposed to hausmannite (Mn₃O₄) at 800°C. Increasing the roasting temperature to 900°C induced a reaction between hematite and hausmannite and led to the formation of a small amount of solid solution of the ferrite spinel MnFe₂O₄. Further increase in temperature to 1000°C led to the formation of a solid solution of braunite (Mn₇SiO₁₂) which decomposed to rhodonite (MnSiO₃) at 1200°C. The magnetic susceptibility of the original ore gradually increased with the roasting temperature, from 0.119 × 10⁻³ at ambient temperature to a maximum value of 80 × 10⁻³ at 1200°C.